You now earn tax revenue on every city that you own! The math is fairly simple. You earn around five Geos each day for every 1,000,000 in value that you possess, paid out every five minutes.

Specifcally, you get ((((YOURTOTALVALUE/24)/12)/1,000,000)*5) every five minutes. This is the total value of your cities, divided by 24 hours, divided by 12 (to get five minutes worth), divided by 1 million, muliplied by 5. Working out as much of this as it mathematically possible, you get (YOURTOTALVALUE/57,600,000) every five minutes.

Just look at it as your total, divided by 1 million, multiplied by 5. This means if you own New York City (current value around 8 million), you'd get about 40 Geos a day.

The downside is that you will soon start having to pay taxes on your armies/troops, but that hasn't been implemented quite yet...